This invention relates to manufacture of semiconductor devices, and more particularly to photoresist burnoff methods of the type used in manufacture of VLSI semiconductor memory devices or the like.
In the manufacture of MOS LSI devices such as dynamic RAMs or the like, a number of photolithography operations are performed which require application of, and subsequent removal of, a photoresist polymer. Dry removal processes are preferred to avoid the problems of using wet chemicals such strong acids, base and peroxides. The dry removal process for photoresist consists of a plasma "ash" or oxygen burnoff; mobile ionic contaminants in underlying silicon oxide layers can result from such burnoff, and this invention is concerned with passivation or elimination of such contaminants problems caused by the contaminants including a flat band voltage shift (i.e., shift in the threshold voltage of MOS transistors in the device) under electrical bias, and temperature stress due to re-positioning the contaminants, either causing degradation in performance of the integrated circuit. The problems are more severe with removal of positive photoresists.
It is the principal object of this invention to provide an improved method of making semiconductor integrated circuits such as memory devices or the like. Another object is to provide an improved method of burning off photoresist in manufacture of such devices.